The present invention relates to a two-for-one twisting spindle with a compressed air operated threading device with which a thread is fed through a thread feeding channel by a jet of compressed air, with a first deflecting surface arranged at an underside of a turntable, disposed above a thread storage disk, and extending radially outwardly from an opening of a radial portion of the thread feeding channel whereby the first deflecting surface has a transition into a second deflecting surface that extends in an upward direction and is convex.
Such a two-for-one twisting spindle is known from EP 00 26 159 B1. With this known device, the jet of compressed air which leaves the thread feeding channel and carries the end of the thread with it is guided against a deflector plate. This deflector is fixedly or adjustably arranged relative to the turntable of the spindle at a position between the outer curved opening of the thread feeding channel and the outer edge of the turntable. The deflector plate is embodied such that its upper end extends at least to the height of the center axis of the outer opening of the thread feeding channel and the extension of its front end surface is essentially tangential to a second deflecting surface which is upwardly curved and convex.
In the above cited publication it is mentioned that the aforementioned device presumably relies on the so-called Coanda effect according to which a jet of air which is guided along a convex curved surface is deflected such that it follows the curvature of the surface.
With the known device, however, the deflection of the air jet is essentially effected by the deflector plate.
The known device has the disadvantage that the deflector plate must be arranged over the entire circumference of the turntable, or an exact position of the outer opening of the thread feeding channel relative to the deflector plate during the threading step, or an adjustment of the deflector relative to the outer opening must be provided in order to be able to perform the threading step. This requires complicated measures and disadvantageous especially for automatic threading.
A further disadvantage of the known device is the soiling and contamination of the surface of the fixedly connected deflector which is not contacted by the thread during the twisting process. Due to fluctuations of the position of the thread balloon, portions of the thread may come into contact with the contaminated surfaces which will result in a reduced quality of the resulting twisted thread.
Another possibility of deflecting a thread without a fixedly arranged deflector is described in DE 29 39 593 C2. In this device a second jet of compressed air is used which deflects the jet of compressed air together with the thread essentially about an angle of 90.degree. in an upward direction. This solution is also rather complicated and requires an exact positioning of the outer opening of the thread feeding channel relative to the second jet of compressed air during the threading step.
It is therefore an object of the present invention to provide a two- for-one twisting spindle with the aforementioned features which provides for an automatic threading of the thread without providing a deflector plate that is fixedly connected relative to the rotatable components of the spindle.